PROJECT SUMMARY Mucosal surfaces must allow the exchange of metabolites required for life into the host and excretion/exclusion of wastes and toxins out of the host, while also maintaining a first line of defense against invasive microbes. However, mucosal inflammation, elicited to combat microbial infection, can also damage the integrity of the mucosal barrier, if not controlled. Many mucosal surfaces are in constant or transient contact with microbes, yet the molecular mechanisms governing the extent of the inflammatory response at the mucosal surface, the healing of the surface after insults and the molecular basis of remodeling changes that affect subsequent mucosal function and inflammatory responses are poorly understood. This proposal will investigate these mechanisms by assembling an experienced team of investigators with diverse and complimentary expertise to further our understanding of the mucosal immune defense mechanisms of the urinary bladder against bacterial infection. Analysis of the bladder mucosal responses to the most common cause of urinary tract infection (UTI), E. coli, in distantly related inbred mouse strains has identified patterns of response that correlate with resistance or susceptibility to both initial and secondary infections. The proposed research will probe differences in the immune defense pathways of the bladder mucosa during acute and recurrent infection, providing critical insights in the field of mucosal immunology and the role of epithelial cells in mucosal response. These studies will specifically investigate the role of bladder mucosal remodeling in modulating innate signaling pathways in previously infected mice (Aim 1) and investigate the protective (Aim 2) and damaging (Aim 3) mechanisms of the acute bladder inflammatory response in nave mice. These responses correlate with outcomes of disease and subsequent remodeling of the bladder tissue, which in turn affects subsequent infections. Understanding immune responses of previously infected vs. nave mucosal tissues will likely give important insights into clinical disease, in which patients over their life-time have undoubtably suffered from multiple sequential infections. These investigations will reveal new details of the mechanisms of mucosal defense against bacteria, broadening the understanding of the regulation of mucosal inflammation and the signaling between mucosal epithelia and immune cells, and thus advance our understanding of acute and recurrent infection susceptibility and protection, in this age of increasing microbial antibiotic resistance. These insights will contribute to the development of novel vaccines and immunomodulatory therapeutics targeting the mucosa.